1. Field of the Invention
The invention relates to a method of sulfonating and somewhat more particularly to a method of sulfonating or sulfating petroleum feed stocks which promotes a high yield of petroleum sulfonates and to the resultant products.
2. Prior Art
A great number of processes have been advanced in this art in attempts to efficiently and economically provide petroleum sulfonates. These usually involve a batch process operation and/or an incremental treatment (quasi-continuous) of various oil feed stocks with concentrated sulfuric acid, oleum or other sulfonating agent with generally a very low yield of desired sulfonated product per contact and relatively large amounts of unwanted reaction by-products. (For a general discussion of the state of the art, see Industrial and Engineering Chemistry, Gilbert et al, Vol. 49, No. 1, Jan. 1957, pages 31-38.)
Many batch processes involve the use of relatively high concentrations of solvents or diluents for achieving a somewhat homogeneous distribution of reactants within the batch and/or the use of multiple contact sequences with progressively increasing severity of sulfonation conditions. This usually involves increased costs since solvents and the like must be recovered, and higher temperatures, longer contact time, increased process costs, etc. In order to increase productivity rates and lower process costs and manpower expenditures, attempts have been made to continuously sulfonate petroleum oils. However, while it is possible to sulfonate a small fraction of the sulfonatable or sulfatable components present in various petroleum oils, attempts to raise the yield, or to increase the extent of reaction, for example, to that hypothetically possible, have been unsuccessful, particularly on the basis of a single cycle or contact.
A special problem has been found in attempting to sulfonate petroleum and/or fractions thereof (both of which, as is well known, typically comprise a complex mixture of various organic materials), in contradistinction to readily sulfonatable chemicals which are of relatively uniform composition, such as dodecylbenzene, ethoxylated alcohols, etc. When one attempts to drive a sulfonation reaction to completion with petroleum oils, such as by adding increased amounts of sulfur trioxide approaching a mol-for-mol basis, based on the sulfonatable components present in a petroleum oil, charring, oxidation, sludge formation and/or substantial polysulfonation occur in the reaction vessel, such as in a tubular reaction vessel, to the point where the vessel becomes plugged and continuous processing becomes impractical or impossible. Even in instances where the reaction vessel remains functional, the resultant reaction product is either of only limited utility or must be further purified or treated to remove solid-like particles therein and render at least some portion of the reaction product useful as a liquid. As an example, when one attempts to sulfonate a petroleum oil containing, say, about 40 to 45% by weight of sulfonatable components, in general, the best that one can achieve with heretofore available processes is a yield of about 10% sulfonated materials, or roughly a 25% conversion.
Typically, petroleum sulfonates heretofore available comprised by-product mahogany sulfonates which are produced by treating petroleum lubricating raffinates or other petroleum fractions with oleum (SO.sub.3 dissolved in sulfuric acid) under controlled time-temperature conditions so that the aromatic portion of the lubricant stock forms by-product organic sulfonates (oil-soluble mahogany acids and water-soluble oil insoluble green acids), leaving mineral white oil, which is recovered after removal of the sulfonates. Additional details for white mineral oil manufacture may be found in Erich Meyer "White Mineral Oil and Petroleum and Their Related Products" (Chemical Publishing Co., Inc., N.Y.) 1968. The organic sulfonates so produced contain appreciable quantities of "sludge," generally comprised of viscous water-soluble (oil insoluble) organic sulfonates which are a mixture of polysulfonates and low equivalent weight monosulfonates. The sludge must be removed from the mahogany sulfonates before a commercially acceptable product can be obtained. However, typical green acid "sludge" yields are manyfold greater than oil-soluble mahogany sulfonates.